1. Parsing and Syntax

2. Syntactic Formalisms: Historic Perspective “Syntax” comes from Greek word “syntaxis”, meaning “setting out together or arrangement” Early grammars: 4th century BC – Panini compiled Sanskrit grammar Idea of constituency – Bloomfield (1914): method for breaking up sentence into a hierarchy of units – Harris (1954): substitutability test for constituent definition Formal work on Syntax goes back to Chomsky’s PhD thesis in 1950s * Some slides in this lecture are adapted from slides of Michael Collins

3. Syntactic Structure

4. A Real Tree

5. What can we Learn from Syntactic Tree? Part-of-speech for each word (N=noun, V=verb, P=preposition) Constituent structure Noun phrase: “the apartment” Verb phrase: “robbed the apartment” Relationship structure “the burglar” is the subject of “robbed”

6. Context-Free Grammars

7. A Context-Free Grammar for English

8. Left-Most Derivation

9. Derivation Example

10. Properties of CFGs

11. Ambiguous Sentence

13. More Ambiguity

14. Syntactic Ambiguity Prepositional phrases They cooked the beans in the pot on the stove with handles. Particle vs preposition The puppy tore up the staircase. Complement structure She knows you like the back of her hand. Gerund vs. participial adjective. Visiting relatives can be boring Modifier scope within NPs Plastic cup holder (examples are compiled by Dan Klein)

15. Human Processing Garden Path: The horse raced past the barn fell. The man who hunts ducks out on weekends Ambiguity maintenance Have the police … eaten their supper? come in and look around taken out and shot

16. A Probabilistic Context-Free Grammar

17. Example

18. Properties of PCFGs

19. Deriving a PCFG from a Corpus

20. Algorithms for PCFG

21. Chomsky Normal Form

22. A Dynamic Programming Algorithm for the Max

23. A Dynamic Programming Algorithm for the Max (cont.)

25. Runtime

26. A Dynamic Programming Algorithm for the Sum

27. A Dynamic Algorithm for the Sum (cont.)

28. A Dynamic Programming Algorithm for the Sum (cont.)

29. Weaknesses of PCFGs Lack of sensitivity to lexical information Lack of sensitivity to structural frequencies

30. PP Attachment Ambiguity

32. Structural Preferences: Close Attachment